Section 12 Serial Communication Interface (SCI)
Rev. 3.00 Mar. 14, 2006 Page 405 of 804
REJ09B0104-0300
12.4
Operation in Asynchronous Mode
Figure 12.2 shows the general format for asynchronous serial communication. One frame consists
of a start bit (low level), followed by transmit/receive data, a parity bit, and finally stop bits (high
level). In asynchronous serial communication, the communication line is usually held in the mark
state (high level). The SCI monitors the communication line, and when it goes to the space state
(low level), recognizes a start bit and starts serial communication. Inside the SCI, the transmitter
and receiver are independent units, enabling full-duplex communication. Both the transmitter and
the receiver also have a double-buffered structure, so that data can be read or written during
transmission or reception, enabling continuous data transmission and reception.
LSB
Start
bit
MSB
Idle state
(mark state)
Stop bit
0
Transmit/receive data
D0
D1
D2
D3
D4
D5
D6
D7
0/1
1
1
1
1
Serial
data
Parity
bit
1 bit
1 or 2 bits
7 or 8 bits
1 bit or
none
One unit of transfer data (character or frame)
Figure 12.2 Data Format in Asynchronous Communication
(Example with 8-Bit Data, Parity, Two Stop Bits)
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Содержание H8SX series
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